1. Field of the Invention
The present invention relates to a mold for injection molding a precision molded article such as an optical disk, which has an air nozzle for peeling the molded article off the mold.
2. Description of the Related Art
In general molding, a protrusion pin is used to take out a molded article from a mold. In contrast, a precision molded article such as an optical disk is peeled off a mold by air, because the quality of the resulting molded article is influenced by the good and bad of the peel-off of the molded article from the mold.
A technique for peeling a molded article off a mold by air is known from, for example, Japanese Patent Laid-Open Publication No. HEI-6-71656 entitled "MOLDING APPARATUS AND METHOD". The conventional molding apparatus comprises a molding section, a mold disposed remotely from the molding section and composed of a stationary mold half and a movable mold half, and air piping branched within the molding section into two pipes which are respectively connected via air blow ports to the stationary mold half and the movable mold half and opening into the mold halves. An air open/close valve and a pressure regulator are connected to the branched pipes inside the molding section so that the stationary and movable mold halves can be air-controlled independently. The pressure regulator comprises a check valve, a surge tank spaced from the check valve, and a pressure adjusting section branched off from the surge tank.
In the conventional apparatus thus arranged, since the molding section is large-sized due to various valves provided therein, it has to be disposed remotely from the mold. In addition, it becomes necessary for the air blow ports to be formed of a relatively long pipe.
Using the conventional molding apparatus arranged as explained above, the present inventor has made an attempt to injection mold an optical disk substrate. However, it was found that since the intended peeling starts with a delay from the feed of an air blow signal, there often occurs incomplete or uneven peeling which leads to undesired deformation of the resulting molded article.
In a continued research to overcome the foregoing problem, the present inventor has found that because the molding section is positioned distantly from the mold, the volume of a flow passage within the piping connecting the mold section and the mold become large, thereby causing the flow passage space to take time to be filled with air of a predetermined pressure. It is also assumed that since it is a gaseous body capable of being compressed, air flows turbulently through such a volumetrically-large flow passage.
With a prospect that the foregoing problem can be solved by minimizing the volume of the flow passage, an experiment was carried out which ended up proving the prospect. This has lead to the present invention.